Depressive disorders occur in Parkinson's disease in about 40%. They often manifest--not seldom preceding diagnosis of Parkinson's syndrome--like monopolar depression. Their cause has not yet been explained in a satisfactory way. Neurotransmitter disturbances are discussed as well as psychogenic factors. There seems to be a subtype of Parkinson's disease with more frequent depression, which is characterized by increased rigidity and bradykinesia, lower age at onset and family history of Parkinson's disease. Especially antidepressants, but also sleep deprivation and electroconvulsive therapy are efficient. The review is illustrated by a case report.